Which visual component provides a connection between data series in a chart?

The legend serves as a critical visual component in a chart, providing a means to understand the relationship between different data series represented within that chart. It typically contains labels or descriptions that correspond to various colors or patterns used in the chart, allowing viewers to discern what each series of data represents. By including the legend, the audience can easily interpret the data and see how multiple series relate to one another, making it easier to draw conclusions based on the information presented. This connection is vital for effective communication of data insights, as it facilitates a clearer understanding of the comparative metrics being displayed.